The present invention relates to a cardiac ablation instrument for endo or epicardial ablation of tissue for the treatment of cardiac conditions, and, in particular, to a handheld cardiac ablation instrument which provides uniform radiation. Methods of ablating cardiac tissue are also disclosed.
Cardiac rhythm irregularity, i.e., fibrillation, is a pathological condition of the heart muscle that can be present in either the atria or the ventricles. Atrial fibrillation is an atrial arrhythmia characterized by rapid randomized contractions of the atrial myocardium, causing an irregular, often rapid ventricular rate. The regular pumping function of the atria is replaced by a disorganized, ineffective quivering caused by chaotic conduction of electrical signals through the upper chambers of the heart. Atrial fibrillation is often associated with other forms of cardiovascular disease, including congestive heart failure, rheumatic heart disease, coronary artery disease, left ventricular hypertrophy, cardiomyopathy or hypertension.
Ventricular Tachycardia (fibrillation) is an arrhythmia characterized by fibrillary contractions of the ventricular muscle due to rapid repetitive excitation of the myocardial fibers without coordinated contraction of the ventricles. The ventricles beat at an abnormally rapid rate, significantly interfering with the pumping of oxygenated blood throughout the body. When this occurs, the ventricles lack sufficient time to fill with blood prior to each contraction. As a result, less blood is pumped out of the heart and less oxygen is carried to the tissues and organs of the body.
Several different ablation techniques are known for treating cardiac arrhythmias. A common technique, known as the Maze technique, requires open chest surgery to segment the atrial tissue in a manner that prevents the heart from sustaining the atrial fibrillation. By providing linear ablations at selected locations in the atrial tissue, electrical conductivity from one segment to another can be blocked and the resulting segments become too small to sustain the fibrillatory process on their own.
Conventional instruments employ a radio frequency ablating device having multiple electrodes with gaps between each electrode. These instruments require careful delivery of energy to the surgical site in order to form long, thin lesions in the heart tissue. The lesions must be well defined within the heart to be effective. The gaps in between the electrodes create a break in the energy, thereby creating a potential for gaps in the lesion pattern, which are known to be proarrhythmic and can lead to atrial flutter. In addition, if the energy is not uniformly transmitted to the target site, hot spots can form causing severe tissue damage or blood coagulation (clots).
Accordingly, there exists a need for a cardiac ablation instrument that provides uniform radiation along a curved path with minimal risks of tissue damage, coagulum formation, and overheating.
The present invention is directed to a hand held cardiac ablation instrument for irradiating a target ablation site. The hand held instrument is especially useful in open chest or port access cardiac surgery for rapid and efficient creation of circumferential and curvilinear lesions. The invention is useful for performing both endocardial and epicardial ablations. The instrument is designed to create lesions in the atrial tissue in order to electrically decouple tissue segments on opposite sides of the lesion. The hand held instrument can include at least one light transmitting optical fiber and a light diffusing element which creates the circumferential or curvilinear lesion. The light diffusing element can be resiliently deformable. A handle is provided for manual application. The handle can be substantially coaxial or otherwise aligned with the center of the circumferential housing.
In one aspect of the invention, an instrument is disclosed that permits uniform irradiation along a curved surface on a hand held device. Light travelling through the light transmitting optical fiber or fibers is scattered in a circular pattern by the light diffusing element. The light diffusing element can include a scattering medium and a reflective end cap that interact to provide a substantially uniform distribution of laser radiation throughout the curvilinear target region. The light diffusing element can also include a reflective coating applied to one side of the light diffusing element such that the coating lies substantially diametrically opposed to the target ablation site.